It is known that prior art flexure pivots may be configured as a cantilevered design (FIG. 1A) or a double ended design (FIG. 1B). In both cases, the primary biasing component of such a flexure pivot is a set of springs that are mounted in an “X” fashion, as best seen in FIG. 2. The springs mount to circular quarter segments, commonly referred to as quads, to form a core. The core of the flexure pivot is formed by bonding the edges of the springs to the quads. Bonding is often accomplished by braising or welding, but other bonding materials and methods may be used.
Current practice requires that the bonding occur in two steps, namely, during the assembly of the core and during final assembly of the flexure pivot. During core assembly, the quads and springs must be carefully assembled and held using a temporary technique that does not interfere with the bonding step. This is typically a delicate process requiring great care. Bonding permanently joins the core assembly. Structurally this is an important step because the joints between the quads and the springs must effectively support all of the loads that are applied to the flexure pivot in service. The cross-section of these joints is relatively small which further raises the priority of these joints.
Once the core is successfully bonded, clearances called undercuts must be machined into the outer diameter of the core, as best seen in FIG. 3. Machining of the undercuts requires a special eccentric machining technique in order to generate the proper shape so that the clearances are only created in places that allow flexure in specific places. Forming and aligning the undercuts is a delicate process requiring close alignment for proper pivot function. The core is then mounted into a sleeve (shown in FIGS. 1A and 1B), which serves as the mounting interface for applications where the finished flexure pivot is used. The core must be bonded to the sleeve to form a unit, which requires a second fixturing and bonding process. After the core is bonded to the sleeve, the unit must be sawed to length and the sleeve must be split. After splitting the sleeve, the unit becomes flexible, thereby forming one of the prior art flexure pivots shown in FIGS. 1A and 1B.
The processes required to build a prior art flexure pivot has a significant number of challenges that make it expensive, limits the materials of construction, and limits the size and configuration of potential products the flexure pivot may be used with. There are several prior art flexure pivots that integrate the quads with the sleeve, but these require generating complex parts that still require careful alignment and assembly for proper operation.
There are a number of challenges presented by the construction of prior art flexure pivots. One of these challenges is that the thickness of the springs defines the strength and flexibility of the flexure pivot. This requires that the springs be precision rolled to the required thickness. Not all materials are suitable for rolling into thin sections and to a tight tolerance. This severely limits number of available materials that may be used to form the springs. Moreover, the need to roll the material in a batch type process to form the springs requires that the spring material be produced in large quantities relative to common customer demand. Applications requiring small quantities of special material suffer because excess material must be purchased in order to support the rolling process, adding significant cost to the project.
Another challenge presented with respect to prior art flexure pivots relates to the braising of the components during the assembly process. Braising, which is often used to bond the components, requires high processing temperatures. The high braising temperatures is often in the heat treatment range of the spring material. Therefore, the braising temperature and heat treat temperature of the spring material must be compatible to avoid affecting the structural integrity of the spring material. This requirement severely limits the number of spring and braising materials that can be mated together.
In addition, the assembly of the quads to the flat springs and cylindrical sleeves is labor intensive and sensitive to proper positioning. This increases the assembly cost and limits the array of applications that can justify the benefits of using a prior art flexure pivot. Also, assembly of the springs to the quads becomes increasingly challenging as parts get smaller. This combined with the nearly fixed size of human hands limits the smallest scale that can use this construction, which is currently about ⅛″ diameter.
In some cases, the springs are welded to the quads during the assembly process. One of the weaknesses of this technique is that the weld must be buried within the section of the quad. This requires that a notch remain where the spring enters the quad interface. Structurally this penetration resembles a crack, which increases local stress and limits the fatigue life of a welded flexure pivot of this construction.
Another challenge related to prior art flexure pivots is that the cutting and shaping of the quads requires dedicated stamping and shaping tools. This requirement limits low volume, custom application of pivots of this construction. While classical construction of flexure pivots is best suited for cylindrical exterior shapes, often applications require custom shapes or features in order to register the flexure pivot to mating parts of a final assembly. Integration of special features on flexure pivots requires intricate machining in order to produce the special shapes. This proves to be expensive which limits the array of applications that can justify use of a prior art flexure pivot.
As such, there is a need for a flexure pivot that enhances manufacturability, increases material options, reduces cost by facilitating automation techniques, and is dimensionally scalable to enhance the size range that the flexure pivot can be applied. The present invention addresses these needs as well as other needs.